Non-volatile memory devices, such as flash memory, are capable of retaining stored charge without power from an external power supply. A flash memory comprises an array of memory cells, each of which is configured to store one or more bits of information corresponding to a charge or gate threshold voltage. For example, new flash memory devices can store several bits per cell and utilize parameters that can exhibit more than two distinct levels. Flash memory devices are typically of two types depending on their structure for storing charge. A floating gate type flash memory stores charge in a floating gate electrode disposed under a control gate electrode. However, the conductive floating gate electrodes need to be electrically isolated for data retention, and the gate structures have a high aspect ratio that can be difficult to manufacture. Also, the density of such flash memory devices increases, the spacing between adjacent memory cells decreases resulting in electrical coupling between adjacent floating gate cells which reduces charge retention time.
A charge trap type flash memory can be manufactured with fewer and less complicated steps than floating gate memory devices. Charge trap memories use a gate insulating layer formed of a material such as silicon nitride, which provides charge trap sites. However, as these devices become smaller, the net area available on a substrate to create an individual charge trap cell decreases. Accordingly, the number of electrons that may be loaded onto a charge trap layer also decreases. This decrease in charge trap cell capacity decreases the amount of information that may be stored by each unit cell.
For various reasons that include these and other deficiencies, and despite the development of various flash memory devices, further improvements in memory devices and charge trap devices are continuously being sought.